The "is not None" is important when checking a variable that may contain a ClauseElement, precisely because ClauseElement defines that __bool__ method.
However, in Session.get_bind(), "mapper" is not supposed to contain a ClauseElement. It should either be an instance of sqlalchemy.orm.mapper.Mapper, or None, in which case "if mapper:" is a valid and concise way to write it. Comparing to None might be strictly more accurate, but it shouldn't be necessary. Simon On Fri, Oct 20, 2017 at 3:17 PM, Антонио Антуан <a.ch....@gmail.com> wrote: > Really, `mapper` contains this: <sqlalchemy.sql.selectable.CTE at > 0x7fe673fb0a50; group_getter>. But does it changes something? I already > encountered this problem in my code, when I checked sqla-objects existance > without "is not None", project was broken. Is it normal to omit that > condition in sqlalchemy code? > > I use: >>>> sqlalchemy.__version__ > '1.0.19' > > пятница, 20 октября 2017 г., 16:42:23 UTC+3 пользователь Simon King написал: >> >> On Fri, Oct 20, 2017 at 2:15 PM, Антонио Антуан <a.ch...@gmail.com> wrote: >> > Hi. >> > I use my own `RoutingSession` and `RoutingQuery` implementation, most of >> > it >> > inspired by `sqlalchemy.ext.horizontal_shard`: >> > >> > class RoutingSession(Session): >> > def get_bind(self, mapper=None, clause=None, shard_id=None, >> > **kwargs): >> > original_bind = None >> > try: >> > original_bind = super(RoutingSession, self).get_bind(mapper, >> > clause) >> > except UnboundExecutionError: >> > # may not be bound >> > pass >> > if shard_id is None: >> > shard_id = TenantIDStorage.get_shard_id() # just global >> > storage >> > bind_for_shard = self.__binds[shard_id] >> > if original_bind is not None and original_bind.url == >> > bind_for_shard.url: >> > return original_bind >> > else: >> > return bind_for_shard >> > >> > def __init__(self, shards=None, query_cls=CachingQuery, >> > engines_factory=None, **kwargs): >> > super(RoutingSession, self).__init__(query_cls=query_cls, >> > **kwargs) >> > self.__binds = {} >> > self.engines_factory = engines_factory >> > if shards is not None: >> > self.update_shards(**shards) >> > >> > def _add_bind(self, key, bind): >> > self.__binds[key] = bind >> > >> > >> > >> > >> > class RoutingQuery(Query): >> > def __init__(self, *args, **kwargs): >> > super(RoutingQuery, self).__init__(*args, **kwargs) >> > self._shard_id = TenantIDStorage.get_shard_id() >> > >> > def get(self, ident): >> > self._check_bound_to_shard() >> > return super(CachingQuery, self).get(ident) >> > >> > def _check_bound_to_shard(self): >> > if self._shard_id is None: >> > raise ValueError('query not bound to any shard') >> > >> > def _execute_and_instances(self, querycontext): >> > self._check_bound_to_shard() >> > querycontext.attributes['shard_id'] = self._shard_id >> > result = self._connection_from_session( >> > mapper=self._mapper_zero(), >> > shard_id=self._shard_id).execute( >> > querycontext.statement, >> > self._params >> > ) >> > return self.instances(result, querycontext) >> > >> > >> > >> > >> > >> > >> > Sometimes I got this error: >> > >> > File "/home/anton/Projects/proj/admin/proj/admin/views/stats.py", line >> > 898, in _get_filters_from_request >> > control_groups = [g.id for g in >> > User.get_own_groups_query(current_user.id)] >> > File >> > >> > "/home/anton/Projects/proj/.venv/lib/python2.7/site-packages/sqlalchemy/orm/query.py", >> > line 2802, in __iter__ >> > return self._execute_and_instances(context) >> > File >> > >> > "/home/anton/Projects/proj/core/proj/core/orm_extensions/rouing_session.py", >> > line 105, in _execute_and_instances >> > shard_id=self._shard_id).execute( >> > File >> > >> > "/home/anton/Projects/proj/.venv/lib/python2.7/site-packages/sqlalchemy/orm/query.py", >> > line 2806, in _connection_from_session >> > **kw) >> > File >> > >> > "/home/anton/Projects/proj/.venv/lib/python2.7/site-packages/sqlalchemy/orm/session.py", >> > line 984, in connection >> > bind = self.get_bind(mapper, clause=clause, **kw) >> > File >> > >> > "/home/anton/Projects/proj/core/proj/core/orm_extensions/cachingquery.py", >> > line 279, in get_bind >> > original_bind = super(RoutingSession, self).get_bind(mapper, clause) >> > File >> > >> > "/home/anton/Projects/proj/.venv/lib/python2.7/site-packages/sqlalchemy/orm/session.py", >> > line 1336, in get_bind >> > if mapper and mapper.mapped_table.bind: >> > File >> > >> > "/home/anton/Projects/proj/.venv/lib/python2.7/site-packages/sqlalchemy/sql/elements.py", >> > line 539, in __bool__ >> > raise TypeError("Boolean value of this clause is not defined") >> > TypeError: Boolean value of this clause is not defined >> > >> > >> > >> > >> > I found that `mapper` in original `get_bind` always checks with `is not >> > None` condition. There is only one place where condition omitted: `if >> > mapper >> > and mapper.mapped_table.bind...`. >> > Possibly it is not correct? Or my code does not do something important? >> >> Are you able to catch this error in a debugger? >> >> I'm going to make a wild guess that "mapper" at this point is some >> sort of SQL construct (such as a column object or mapped property), >> rather than an actual mapper. >> >> You don't say which version of SQLAlchemy you are using, but since >> you've overridden _execute_and_instances, I wonder if you need to use >> something like query._bind_mapper() as used by _get_bind_args: >> >> >> <https://bitbucket.org/zzzeek/sqlalchemy/src/4b22b01ade6f94cc4db2f2040c802067a25d29a4/lib/sqlalchemy/orm/query.py?at=rel_1_1_14&fileviewer=file-view-default#query.py-2872> >> >> Hope that helps, >> >> Simon > > -- > SQLAlchemy - > The Python SQL Toolkit and Object Relational Mapper > > http://www.sqlalchemy.org/ > > To post example code, please provide an MCVE: Minimal, Complete, and > Verifiable Example. See http://stackoverflow.com/help/mcve for a full > description. > --- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to sqlalchemy+unsubscr...@googlegroups.com. > To post to this group, send email to sqlalchemy@googlegroups.com. > Visit this group at https://groups.google.com/group/sqlalchemy. > For more options, visit https://groups.google.com/d/optout. -- SQLAlchemy - The Python SQL Toolkit and Object Relational Mapper http://www.sqlalchemy.org/ To post example code, please provide an MCVE: Minimal, Complete, and Verifiable Example. See http://stackoverflow.com/help/mcve for a full description. --- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. 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